Super Jet Are dual sbn 44's on 710cc overkill?

[hydrostyler]

I'm starting over on my top end. Was previously running a stock sleeved 61x bored to 84mm. It's now in need of a bb sleeve job and pistons etc. I'm throwing a new 81.5mm top end with pump gas domes in and gonna run that for the season. The rest of the motor consists of a 62t bottom end, R&D dual intake with spacer, dual sbn 44's, a mod B-pipe, lightened flywheel, msd enhancer, modified kawi reed cages. Am I gonna have tuning issues with the dual 44's on 710cc's? I've often though about running a single 44 for easier tuning anyway. Anyone use the 62t single manifold selling on eBay for around $250? Just fishing for ideas. Thanks.

 

[eeerieski]

I'm starting over on my top end. Was previously running a stock sleeved 61x bored to 84mm. It's now in need of a bb sleeve job and pistons etc. I'm throwing a new 81.5mm top end with pump gas domes in and gonna run that for the season. The rest of the motor consists of a 62t bottom end, R&D dual intake with spacer, dual sbn 44's, a mod B-pipe, lightened flywheel, msd enhancer, modified kawi reed cages. Am I gonna have tuning issues with the dual 44's on 710cc's? I've often though about running a single 44 for easier tuning anyway. Anyone use the 62t single manifold selling on eBay for around $250? Just fishing for ideas. Thanks.

I've read that dual 44's are not necessary unless you are running a big bore motor or if you are racing with the engine pinned at high rpms. That being said the tuning for dual 44's will be slightly harder than dual 38's and doubly more difficult than a single 44/46 carb. I have that single intake manifold on my 705 and it works fine, I found a used one on here for $100 though, it needs re-anodized and some proper fasteners though. It is just a single 44mm manifold for a kawasaki 650 with an adapter plate. If you are handy you could get the kawi manifold and make an adapter plate.

 

[wanderer1]

I run dual 44's on my wifes 710 B1 and 38's on my 718 B1. She starts walking away from me almost right away

 

[Matt_E]

I've read that dual 44's are not necessary unless you are running a big bore motor or if you are racing with the engine pinned at high rpms. That being said the tuning for dual 44's will be slightly harder than dual 38's and doubly more difficult than a single 44/46 carb. I have that single intake manifold on my 705 and it works fine, I found a used one on here for $100 though, it needs re-anodized and some proper fasteners though. It is just a single 44mm manifold for a kawasaki 650 with an adapter plate. If you are handy you could get the kawi manifold and make an adapter plate.

Why is tuning dual 44's harder than dual 38's?
Why is it doubly more difficult than a single? (Hint: It's more work - once - but not more difficult)

OP: I'd stick with stock or modified dual 38's for a 701. They work great. However, since you already have the 44's - just use those. They'll work fine. You won't have tuning issues. Generally speaking, the larger carbs will have a more pronounced hit than smaller carbs, which are more linear.

 

[steve-uk]

Anyone use the 62t single manifold selling on eBay for around $250?

as an aside i sell the atp single intake manifolds for $225

 

[Freakrider]

Is your manifold epoxied to increase air velocity/carb signal of the 44's ?

 

[swapmeet]

as an aside i sell the atp single intake manifolds for $225

 

[hydrostyler]

Alright guys, thanks for the info. I will go ahead and run the dual 44's and see how they work. Jump On It , speaking of epoxying manifolds and what not, would it be of much benefit to fill in the fingers on my cases? I previously ported the upper areas of the intake, but did not fill the fingers. I'm not really chasing horsepower anymore, I just want the ski tuned to be responsive and reliable. As I get older I enjoy riding more than wrenching.

 

[kevbo]

Performance wise, the pipe will hit a little harder with 44s. They will need a much richer part throttle and/or full throttle mixture to get best response. This means it will need to sputter a lot around 1/4 throttle and/or be well rich of peak full throttle rpm. For cruising or long full throttle runs the 38s will go just as fast and ultimately burn less fuel because they can be tuned leaner without losing response. You will never realize best performance without learning to tune the carbs and pump.

 

[wanderer1]

Performance wise, the pipe will hit a little harder with 44s. They will need a much richer part throttle and/or full throttle mixture to get best response. This means it will need to sputter a lot around 1/4 throttle and/or be well rich of peak full throttle rpm. For cruising or long full throttle runs the 38s will go just as fast and ultimately burn less fuel because they can be tuned leaner without losing response. You will never realize best performance without learning to tune the carbs and pump.

Very true about the 44's, just idleing and putting around not really brapping they sputter and I get some vibration I cant tune out, but get on the pipe and they rip

 

[Freakrider]

Alright guys, thanks for the info. I will go ahead and run the dual 44's and see how they work. Jump On It , speaking of epoxying manifolds and what not, would it be of much benefit to fill in the fingers on my cases? I previously ported the upper areas of the intake, but did not fill the fingers. I'm not really chasing horsepower anymore, I just want the ski tuned to be responsive and reliable. As I get older I enjoy riding more than wrenching.

Since your ski is back together, you could run R&D case stuffers instead of the filling the fingers...I run those in a fully XS ported motor/exhaust 735cc with 44's and the intake manifold is epoxy ramped to increase signal; reed stuffers too. Once the carbs are jetted properly and dialed in the 44's are very clean/responsive at all speeds...

 

[eeerieski]

Why is tuning dual 44's harder than dual 38's?
Why is it doubly more difficult than a single? (Hint: It's more work - once - but not more difficult)

OP: I'd stick with stock or modified dual 38's for a 701. They work great. However, since you already have the 44's - just use those. They'll work fine. You won't have tuning issues. Generally speaking, the larger carbs will have a more pronounced hit than smaller carbs, which are more linear.

Dual 44's have less signal at low rpm's, thus harder to get spot on (for tuning the low circuit) and lit looks like others above me have lacking low rpm performance. I suppose it is only slightly more difficult to do 2 instead of one.

 

[Freakrider]

Dual 44's have less signal at low rpm's, thus harder to get spot on (for tuning the low circuit) and lit looks like others above me have lacking low rpm performance. I suppose it is only slightly more difficult to do 2 instead of one.

That's why you have to increase intake/case tract signal by the three things outlined in post # 11, thanks to Chucky at XS for the guidance on ramping the intake.

 

[hydrostyler]

Ok, so I will start searching for some reed stuffers to boost the low rmp signal. Coming from a mx background, I get frustrated pretty quick tuning ski carbs. I'm used to 2 jets and 1 screw, couple laps around the yard and go riding. With having to tune each step by the 1/4 throttle position, are there any devices or tricks people have used to tune each section? I was thinking about building a throttle lever with an adjustable stop or atleast an indicator to let me know where I'm at for each stage. I have a mikuni manual and printed out a tunung for dummies type write up and I understand each step while I'm reading it. Its just the throttle positions themselves that make it tough for me. One last thing, the dual 44's I have, I bought used years ago, they have "MAC 52" stamped at the base of each of them, and I recall the guy talking about them being better than stock??? Are they some race purpose carbs that are gonna give me fits getting them dialed in for everyday riding? I usually get the top end solid, but the bottom end is always lacking.

 

[kevbo]

Ok, so I will start searching for some reed stuffers to boost the low rmp signal. Coming from a mx background, I get frustrated pretty quick tuning ski carbs. I'm used to 2 jets and 1 screw, couple laps around the yard and go riding. With having to tune each step by the 1/4 throttle position, are there any devices or tricks people have used to tune each section? I was thinking about building a throttle lever with an adjustable stop or atleast an indicator to let me know where I'm at for each stage. I have a mikuni manual and printed out a tunung for dummies type write up and I understand each step while I'm reading it. Its just the throttle positions themselves that make it tough for me. One last thing, the dual 44's I have, I bought used years ago, they have "MAC 52" stamped at the base of each of them, and I recall the guy talking about them being better than stock??? Are they some race purpose carbs that are gonna give me fits getting them dialed in for everyday riding? I usually get the top end solid, but the bottom end is always lacking.

If the response is always sluggish make sure the pump load is low enough.

 

[hydrostyler]

what are you referring to as "pump load"? the pitch of my impeller(concord 13/17) or pop-off pressure(22psi) in the fuel pump section of the carb?

 

[Polish jet pilot]

he means the pump combo (impeller, nozzle diameter, cone type, how close the prop sits to the vane case..)..

 

[kevbo]

what are you referring to as "pump load"? the pitch of my impeller(concord 13/17) or pop-off pressure(22psi) in the fuel pump section of the carb?

Out of the box Concord 13/17 is too much load. Let IMPROS do their 13-16 mod or just bend the trailing edge yourself. It will make a world of difference.

 

[Polish jet pilot]

kevbo, would 13/16 oem Yama prop (after 2008) be a proper prop for such a setup? Do yo uhave any experience with them...seem like a very good design but would they need modding to be a good freestyle prop?

 

[kevbo]

I have no experience with the stock large hub SJ impeller. It would likely be very good with minor adjustments. I will be testing a 12-18 large hub Solas this summer.